Aniline is widely used in the production of methylene diphenyl diisocyanate (MDI), a key intermediate for polyurethanes and automotive plastics, and is used to produce antioxidants and vulcanization accelerators for rubber, and as an intermediate in the production of herbicides, pesticides, dyes and pigments, among many other uses. Today it is typically produced by catalytic hydrogenation of nitrobenzene, or less commonly, by amination of phenol. Catalytic hydrogenation of nitrobenzene is highly exothermic, having a heat of reaction of about 130 kilocalories per mol. The reaction is carried out commercially in the presence of excess hydrogen in both the vapor phase and the liquid phase. Vapor-phase processes typically employ either fixed-bed or fluidized-bed reactors. Catalysts of palladium or copper on activated carbon or alternate support, often in combination with other metals selected from the group consisting of lead, vanadium, phosphorous, and chromium as modifiers/promoters have proven to be effective for vapor-phase hydrogenation. High activity and selectivity have been obtained with these catalysts. Hydrogenation of nitrobenzene in the liquid phase has been performed with slurry or fluidized-bed reactors. Operating conditions are typically a temperature in the range of from about 90° C. to about 200° C. and pressure in the range of from about 100 kPa to about 600 kPa. In some cases, the liquid phase process utilizes an excess of aniline as the reaction solvent and removes heat produced via the reaction by allowing the reaction mixture to boil off at a reaction pressure usually less than 100 kPa. One catalyst that has been used for the liquid process is finely divided nickel on diatomite. One continuous liquid-phase hydrogenation process is carried out in a plug-flow reactor with a platinum-palladium catalyst on a carbon support, with iron as modifier. The modifier is used to provide good catalyst life, high activity, and protection against aromatic ring hydrogenation.
Toluenediamine (TDA) exists in several isomeric forms. The TDAs are large-volume intermediates used in the production of a wide variety of industrial and consumer products, including explosives (TNT), dyes and plastics. The mixture of 2,4- and 2,6-isomers is used predominantly as an intermediate in the manufacture of toluene diisocyanate. Commercial mixtures of 2,3- and 3,4-isomers, as well as the 2,4- and 2,6-isomers, are used as co-reactants or as raw materials in the manufacture of urethane products, dyes, corrosion inhibitors, and rubber antioxidants. The most commonly marketed isomers and isomer mixtures are 2,4-TDA, 3,4-TDA, m-TDA (an 80:20 or 65:35 mixture of the 2,4- and 2,6-isomers), and o-TDA (3,4-, 2,3-isomers, as 60:40 mixture); 2,5-TDA is also marketed in small quantities. Any single commercial product will contain various levels of the other isomers. TDAs are typically produced from dinitrotoluenes through a liquid phase catalytic hydrogenation process, or by the reaction of iron and hydrochloric acid with the dinitrotoluenes. Byproducts of the reactions include water and organic by-products, which are separated from the TDA product based on their lower or higher boiling points. Most existing processes and production facilities for toluenediamine or aniline are subject to a variety of constraints such as product yield, plant size, energy consumption and mass flow limitations. Accordingly, there is continuing interest in improving the ways that aniline and toluenediamine are produced.